This concerns the development of a process which assures color uniformity, texture and viscosity in the production of paints specially for painting of metal objects, more specifically, car bodies.
Presently, the manufacture of paint by the conventional method involves a quite complex process and is formed by the following phases: weighing of the raw material, preparation, adjustment of color, coverage, adjustment of viscosity, quality control, canning and packaging. The raw materials which are necessary to produce a given color of paint are weighed in the quantities mentioned in a formula, placed on a pallet and taken, by the lifting truck, to the paint manufacturing plant which is awaiting the starting of the production. The raw materials, either solid or liquid, are weighed in different places, far from the production line, and we should point out that the accuracy of such weighed quantities depends upon the scales used which, in turn, should constantly be gauged so that precise results may be achieved in the weighing operations. Some raw material, which are added in large quantities (such as resins and solvents), are taken at the plant preparation area.
All raw materials which arrive at the preparation area are kept in tanks located in dikes. Each tank has its own pump which is driven by the respective feeding valve for raw materials and which is located in the piping which reach the plan, and in said piping system there is coupled a single flow meter which controls the quantity of the raw materials which have to be added to the mixing tank.
Initially, the operator connects one end of a hose to the pipe of the product which is to be added while the other end of the hose is placed against the mouth of the mixing tank, in such a way that in order to unload the raw material, the operator marks in the meter the quantity in weight (Kg) of the product and opens the feeding valve; the valve sends an electric signal to the pump (located in the dike) turning it on and transferring the product from the outside storage tank to the mixing tank, located at the plant and, in this manner, as soon as the quantity marked in the flow meter is reached the pump is automatically turned off.
The preparation phase consists of the addition, one by one, of the raw materials, following a given order and starting always with the products of larger quantity, followed by those of small quantity, with the resin being the first product to be added in the mixing tank, without stirring. It should be noted that if the resin is stored in drums, the operator should use a drum tumbler, which is kept in an appropriate place, taking it next to the mixing tank in order to proceed with the unloading of the resin and, if said resin is taken directly from the pipe system existing in the plant, the procedure is practically the same for the weighing or, if there is a pipe system feeding the plant, the addition process through the flow meter, as mentioned above.
Other products (additives) are added also by hand and under stirring, using pails and cans.
The whole addition work described above takes approximately 4 hours.
The dying or color adjustment process is performed by the manual addition, with use of pails, of the dying additives, with the color technician weighing first the empty pails where the dyes are placed and weighing the pails again when full, in order to identify the volume of concentrate materials which are placed in the tank under stirring, until reaching the appropriate color, with the pails being weighted once again in order to define the exact quantity which was added.
Then a small sample of the paint is taken to the quality control laboratory, which paints a small plate at the painting cabin, with said plate being dried, in open air, for 5 to 30 minutes, and than in a stove, at 60 to 180xc2x0 C. for 10 to 30 minutes, waiting the cooling down of the plate and comparing it with a standard sample, either visually or through instruments. If the color is not within the required standards, the color technician makes the necessary adjustments and repeats the procedure in order to adjust the color until the paint is within the referred standards. Normally, in order to adjust the color, the color technician repeats from 3 to 4 times the above mentioned process and this takes, on average, 4 hours. It should be pointed out that if the color technician adds the wrong dye or in an exaggerated amount, it is impossible to adjust the color and, therefore, the whole lot is lost.
After the adjustment of the color a sample is taken and sent to the quality control department for the adjustment of viscosity and tests. The viscosity adjustment is made on the sample and performed through the identification of the volume of solvent contained in said sample, when the total volume of solvent to be added to the mixing tank is computed.
In this phase, the operator should bring the solvent to adjust the viscosity, weighing the solvent in pails, cans or drums (depending upon the quantity of solvent to be added) and pouring it into the mixing tank. If the use of drums is necessary, a drum tumbler equipment should be used, which is kept in an appropriate place, taking it next to the mixing tank in order to proceed with the unloading of the solvent.
In order to wash the tank or bowl, the operator fills a can with cleaning solvent, taken from the closest solvent pipe, pours it by hand and cleans the walls with a brush. After this starting work, the operator pours more solvent in order to rinse, and this dirty solvent, which comes from the tank or bowl, is drained through a draining cock into a drum, which is taken to the shipping platform of the plant in order to be removed to the so called xe2x80x9csolvent recuperatingxe2x80x9d plant, which distills and recovers the solvent, which is returned to the plant through a pipe system, to be used again.
When the paint is ready, a sample is taken and sent to the quality control department, where the following tests are performed: color, coverage, solids, specific weight and viscosity. Presently, these tests are performed as follows:
Color: is the determination of differences in shade between a film and its respective standard, when looked under natural light and in which a sample is taken out, the viscosity is adjusted and the paint is applied on a steel plate, awaiting for 15 minutes to evaporate the light solvents and, after said period of time, the sample is placed on a stove under 60xc2x0 C. for 30 minutes. The average time for the test is of 1 (one) hour, but in the case of white synthetic enamel, the color technician needs 16 hours for the drying of the paint in open air, and it may take up to 5 days in order to adjust the color and to finish the tests.
Specific weight: used for the determination of the specific mass of liquid paints, solutions and dispersions, the result of which is expressed in g/cm1, being traditionally referred to as density: the method is based upon the relationship between mass of a substance and its volume.
For this, a container, the volume of which is known, is filled with a sample at 25xc2x0 C., the container is weighed obtaining the specific weight, with the average time spent to perform the test being approximately 10 minutes.
Solids: is the percentage of solid material existing in a paint. The content of non volatile material in a product is not an absolute quantity, but depends upon the temperature and time of heating used; the recommended temperature and time is 120xc2x0 C. for 1 hour of stove, and, in this method a fixed quantity of the product is weighed, spread in a container and taken to a stove for 1 hour, after said period, the sample does to the drying oven for 30 minutes and then is weighed in a laboratory scale in order to obtain the percentage of solid material; the average time for said tests is 2 hours. If the percentile value of solids is out of the specified standards, the adjustment is made with the addition of resin or dyes and if during said addition a larger quantity is used, the whole lot is rejected.
Viscosity: in a quite empirical way, it is possible to say that viscosity is the difficulty a liquid offers against its flowing; the method is based upon the flowing time of a continuous flow of a liquid at 25xc2x0 C., through a given diameter hole called Ford 4 glass, and if the solvent is added in large quantities, it is also impossible to adjust the viscosity, therefore losing the whole lot.
Said test takes approximately 30 minutes to be performed.
After the approval by the Quality Control department, the approved paint is placed in cans and then packaged, by hand. The filling of containers may be performed in any quantity, depending on the machine to be used.
The average time needed to achieve the analysis for color, viscosity, solids and specific weight, considering the total time from the moment taken from the production sector, time awaiting for the tests in the laboratory, until the final answer from the Quality Control Laboratory to the production department is of approximately 4 hours.
We should point out further that if the addition of dyes, solvents or resins for the adjustment of color, viscosity and solids are performed in non appropriate quantities by the operator or color technician, it is possible to lose the whole lot, which will be totally eliminated, made by different persons and, considering that there are the aspects of training, capacity, interpretation of results, the analysis depend also of the gouging of the instruments and quality of the laboratory equipment. Finally, there is a series of factors which may affect significantly the results, with implications in quality and in the cost of production.
In the present invention, the continuous and automatic process for the production of automotive paints and others is constituted by a process which produces automatically any type of paint, strictly within the standards specified in the formulae, complying with the requirements of color, coverage, solids and viscosity, allowing also the automatic change of color or type of paint in approximately 3 minutes. The packaging may be made with any volume, depending on the machine to be used for such a work.
For the manufacture of certain types of paint, the mixture of materials is taken into one of the two mixing tanks; while a mixing is loaded and mixing the mixture of the other tank is being continuously pumped into the head of the mixer, which has high speed stirring. Other materials required for the final paint (additives and dyes) are simultaneously pumped within the mixing head in order to be mixed with products of different tanks of raw material. We call raw materials the resins, the concentrates, solvents and additives which are used for the production of paints.
The paint, after being ready, passes through a probe which reads the color and viscosity and then is loaded into cans or drums (0.9, 1.0, 3.6 and 4.0 litters or other volumes) ready for delivery.
The whole manufacture process for paint is performed by the PLC (Programmable Logic Controller) and the system in controlled by the supervisor systems through the LLX-DMACS software, where all necessary information are stored and then used and with said system monitoring the following parameters: Color, Coverage, Viscosity, Specific weight, Pressure, Flow, Dying power of the concentrated.
In summary, this process has the following characteristics: it produces automatically the paint in the specified color and makes the automatic cleaning in approximately 3 minutes. In other words, all pipes, tanks, valves and equipment are totally cleaned in this short period of time and, with this, allows a fast changing of paint (changing the color and/or type of resin) in respect to conventional methods, with great flexibility in the production of paints. Namely, it is possible to produce any color of paint in any resin contained in the tanks of raw materials, without the smallest possibility of contamination of one paint with the other, with the whole color, coverage and viscosity control being performed on line.
Being continuous, the system has the flexibility to produce from small lots up to large ones.
It performs instantaneously the tests of color, solids, viscosity, specific weight along the whole manufacture process, with the tests being performed as the paint is produced. The time for the preparation of the system in order to produce a new lot is extraordinarily small in respect to the conventional process, due to the fact that the system performs the automatic cleaning.
With this system it is possible to achieve perfect reproductions of paints, namely, the process produces always the same paint, as per the standards specified in the formulation.
Considering that this process is made in a continuous and automatic manner, the adjustments are performed with the addition in the exact proportions and continuously, thereby eliminating the addition in larger quantities than the necessary ones and eliminating also eventual problems with the quality of the paint.
Due to the fact that the process is continuous and automatic, there is no need to obtain samples for the laboratory in a manual way, with all the inconvenience mentioned above.
Another important benefit of being a continuous and automatic process is that it is possible to use automation related resources, such as alarms, indication of instant reading, graphs of the parameters, reports, accrued values along the time, history, trends, etc., with the power to speed up and optimize the maintenance of the system providing events based in historic facts, filing problems or changes occurred in the systems etc.
Great reliability of the measuring system, for this being a continuous and automatic system independent of outside variables, such as the waiting time to perform the tests, contamination, etc.
The system is possible to monitor, for all stages of the process and all parameters are duly known and controlled.
The system does not require the same number of operators for maintenance, nor the need of maintaining a laboratory with sophisticated equipment, for the controls are performed on line.
With this process, a great loss of time is avoided in the movement of raw materials for the addition of the products, as it is done in the conventional processes.
Due to the fact that the process is fully automatic, the personnel used in the operation of the plant becomes more specialized and therefore qualified to perform any repair in the plant.